If you wanna lock a file with a password ,you can do so using winrar..1)Right click on the file for which u want the password to be put.
2)Click on "Add to Archive".
3)Then go to Advanced tab.
4)Click on set password and choose ny passwd.
5)Click ok.
6)A winrar file with your filename will be created.
7)Next u may delete the original file,as you have now compressed it with a password.
8)Any one trying to open the rar file wont be able to, unless he knows the passwd.